1. Field of the Invention
The present invention relates generally to a cutting head for a cord type mower. More particularly, the present invention relates to a cord feeding system for extending a cord wound on a bobbin in a rotary casing to a length necessary for mowing.
2. Description of the Related Art
Many conventional cord type mowers have systems in their cutting heads for feeding new cord when the current cord length is insufficient. Also, manual-type cutting heads are known which permit manual extension of the cord wound on a bobbin.
At present, the so called tap-and-go type and automatic type cutting heads are popular. For the tap-and-go type, the cord is feed the required length by releasing an interlock between a bobbin and a rotary casing. The interlock is released either by hitting or strongly pressing the rotary casing against the ground. This type of cutting head is disclosed in, for example, Japanese Utility Model Publication No. 2-16595, Japanese Patent Publication No. 2-26922, U.S. Pat. Nos. 4,161,820, 4,183,138, and 4,189,833.
For the automatic type, the interlock between the bobbin and rotary casing is released by the centrifugal force which changes according to the length of the cord that extends from the rotary casing. Thus, the desired cord length can be maintained. This type of cutting head is disclosed in, for example, Japanese Patent Publication No. 59-22484, Japanese Patent Laid-open No. 60-83508, Japanese Patent Laid-open No. 63-79522, Japanese Patent Laid-open No. 2-163003, U.S. Pat. Nos. 4,347,666, 4,607,431, 4,660,286, and 4,817,288.
For the tap-and-go type, it is necessary for the operator to frequently check the length of the cord consumed during mowing and extend the cord by hitting the rotary casing against the ground at times or strongly pressing it. Otherwise, the mowing efficiency greatly decreases. Therefore, the operator always has to execute checking and hitting. The checking and hitting give a large mental burden and physical load to the operator.
However, the tap-and-go type has the advantage that the operator can freely set the cord length according to the state of the material (such as grass) being cut. For example, when grass is soft, it is possible to improve the operation efficiency by extending the cord length which permits to the cutter to mow at a faster rate. When grass is hard, it is possible to insure that the grass is cut by setting the cord length to a relatively small value, which increases the cutting force of the cord. Therefore, some operators prefer the advantage of optionally setting the cord length according to the situation to the labor saving advantages of the automatic feeding devices.
Automatic type feed mechanism automatically extends the cord after it has been worn to a predetermined length. Because the extending length depends on the characteristics of the elastic body and heavy bob set in the rotary casing, it is limited to a predetermined range. Therefore, to change the extending length, the elastic body and heavy bob should be changed. However, it is very troublesome to change the parts according to the type of operation. Therefore, the cord length is normally preset to an average length required during operation in a variety of situations.
Because the cord is automatically extended when the cord is worn due to mowing, the automatic-type cutting head does not require hitting by the operator and is therefore easier to operate. However, because the operator cannot optionally select the cord length, it is impossible to extend the cord longer than the set length or keep the cord shorter than the set length.
Thus, the tap-and-go type and the automatic type each have their own features. However, each of the features appears as both an advantage or disadvantage. Because the tap-and-go type allows the operator to optionally select the cord length, it easier for professional operators to use because it operates more efficiently.
The tap-and-go type, however, requires the operator to always pay attention to the cord length and also requires that the rotary casing be hit when the remaining cord becomes short. Therefore, during prolonged mowing, this type gives a larger burden and physical load to the operator. Thus, the request (or demand) for the automatic type has recently been increasing in the professional market.